Corrugated structures and method for thermoforming packages

ABSTRACT

A corrugated structure having a first flat layer, a first corrugated layer secured to the first flat layer, a second flat layer having a first side and a second side, wherein the first side is secured to the first corrugated layer on a side opposite of the first flat layer, a coating layer secured to the second side of the second flat layer, wherein the coating layer has a melting temperature of at least about 450 degrees Fahrenheit and chloroform-soluble extractives of at most about 0.5 milligrams per square inch.

BACKGROUND

This application claims priority to U.S. Provisional App. No. 60/489,433 filed on July 23, 2003, the contents of which are hereby incorporated by reference.

The present invention relates to coated corrugated structures that may be thermoformed into packages or containers.

Conventional methods and corrugated structures have been used to form a variety of corrugated packages. Conventional corrugated structures include a base material, an intermediate flute and a liner material. The intermediate flute secures the liner to the base material. In general, a corrugated structure requires less material to form a rigid structure that is as strong as a much thicker single ply structure.

U.S. Pat. No. 6,491,214 to Plummer et al. (assigned to Procter & Gamble) illustrates a conventional corrugated food container. Conventional containers formed from conventional corrugated structures include paper plates, bowls, clamshells, trays and other disposable products. The containers are formed from a corrugated structure blank. The container described in Plummer et al. has three layers or plies. The first layer contacts the food or product placed on the container. The middle layer is a corrugated flute and secures the first layer to the third layer. The third layer forms the support base for the container. The blank is formed or shaped into the container using a conventional technique, such as thermoforming.

A conventional thermoforming technique involves applying heat and mechanical force concurrently to the container blank in a container-forming die. Exemplary container forming equipment is manufactured by Gralex Corporation of Lewis Center, Ohio.

However, the above conventional containers are not suitable for all cooking and manufacturing applications. Accordingly, there is a need for improved thermoformable corrugated structures that allow for flexible manufacturing techniques and practices, and for improved coatings for these structures which exhibit substantial improvement in barrier properties compared to those which have previously been available.

SUMMARY

The present invention describes a coated three layer corrugated structure that provides flexibility in the manufacturing process. One embodiment of the present invention is a structure having a first flat layer, a first corrugated layer secured to the first flat layer, a second flat layer having a first side and a second side, wherein the first side is secured to the first corrugated layer on a side opposite of the first flat layer, a polymeric coating layer secured to the second side of the second flat layer, wherein the polymeric coating layer has a melting temperature of at least about 450 degrees Fahrenheit and chloroform-soluble extractives of at most about 0.5 milligrams per square inch. A second embodiment of the present invention is a similar structure, wherein the said first flat layer comprises a side opposite of the said first corrugated layer which has been coated with a composition to improve its printability (commonly referred to as clay coated). Printing on this improved surface may occur prior to or after the corrugated structure is formed.

Other objects, embodiments and advantages of the present invention will be apparent from the following detailed description, the accompanying drawings and the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention may be better understood with reference to the following drawings. In the drawings, like reference numerals designate corresponding parts throughout the several views. Also, the components in the drawings are not necessarily to scale.

FIG. 1 is a front elevational view, shown in cross-section, of a corrugated structure of the present invention;

FIG. 2 is a front elevational view, shown in cross-section, of the corrugated structure of FIG. 1 without a base layer; and

FIG. 3 is a front elevational view, shown in cross-section, of an alternative embodiment of the corrugated structure of the present invention.

DETAILED DESCRIPTION

The present invention covers a wide range of corrugated packages, containers, vessels and the like formed from the basic corrugated structure 100 illustrated in FIG. 1. A first layer 10 is illustrated as forming the base or outer side 11 of the structure 100. The first layer 10 is essentially flat and can be formed from conventional paper or paperboard materials that provide sufficient strength for the intended structure 100. Exemplary materials for the first layer include solid bleached sulphate (SBS) paperboard material either clay coated or uncoated. Typically, the paperboard has a coating of a liquid suspension of minerals such as coating clay, calcium carbonate, and/or titanium dioxide with starch or an adhesive. This mineral coating is applied to the paperboard surface to smooth the surface. Densification and mechanical polishing (calendering) finish the mineral coated surface to a high degree of smoothness and provide a superior print surface. The first layer 10 could also be bleached or unbleached as desired. A bleached paper or paperboard is desirable when the structure 100 will be used in a cooking application.

Typical basis weights for the first layer 10 are in the range of about 50 pounds per 3,000 square feet to about 140 pounds per 3,000 square feet. Typically, the paperboard substrate used for the first layer 10 has a thickness range of about 0.004 inches to about 0.035 inches. The invention covers the full range of paper or paperboard substrates, as applied to the packaging field and other suitable applications.

The fluted or second layer 20 is any suitable material such as the coated or uncoated paperboard described above for the first layer 10. The second layer is folded or scored to produce a flute, also referred to as corrugation, with ridges 21, 22. The height of the flute is denoted by the letter “H”. Typical flute height sizes includes size “E,” defined as approximately 90 flutes per foot with a chordal height of about 0.043 to about 0.046 inches, although any flute height H providing sufficient strength and adhesion between the various layers 10, 20, 30 is acceptable. Exemplary basis weights for this second layer 20 are in the range of about 50 pounds per 3,000 square feet to about 140 pounds per 3,000 square feet. Typically, the paperboard substrate used for the second layer 10 has a thickness range of about 0.004 inches to about 0.035 inches. The second layer 20 secures the first layer 10 and third layer 30 to each other at the ridge points 21, 22. The first and third layers 10, 30 can be secured using conventional adhesives and techniques. The adhesive can be applied to the flute 20 along the ridge points 21, 22 or along the inner surfaces 12, 31 of the two layers 10, 30.

The third layer 30 is essentially flat and can be formed of conventional paper or paperboard materials that provide sufficient strength for the intended structure 100. Exemplary materials for the third layer 30 includes SBS paperboard material either coated or uncoated. Typical coatings may include clay or other mineral compounds that are typically used to improve the surface of materials. The third layer 30 could also be bleached or unbleached as desired. Typical basis weights for the third layer 30 are in the range of about 50 pounds per 3,000 square feet to about 140 pounds per 3,000 square feet. If needed, other suitable coatings could be placed on the outer side 32 of the third layer 30.

The fourth layer 40 has a surface 42 that is in contact with an article (not shown) placed inside a container (not shown) formed from the structure 100. The fourth layer 40 is any suitable coating such as a polymer coating. One example of a specific coating is a coating suitable for food contact. Exemplary food contact coatings 40 include polyethylene terephthalate (PET) and polymethylpentene (PMP). Suitable coating weight ranges for PET include a coat weight range of about 8 pounds per 3,000 square feet to about 30 pounds per 3,000 square feet with an exemplary range of about 15 pounds per 3,000 square feet or greater. Suitable coating ranges for PMP include a coat weight range of about 5 pounds per 3,000 square feet to about 15 pounds per 3,000 square feet with an exemplary range of about 8 pounds per 3,000 square feet or greater. In an exemplary method the fourth layer 40 is extrusion coated using conventional extrusion methods onto the top surface 32 of the third layer 30. An ideal coating material is mass stable or has a melting point of about 450 degrees Fahrenheit or higher and has chloroform-soluble extractives not exceeding 0.5 milligrams per square inch of the food contact surface.

FIG. 2 illustrates an alternative embodiment of the present invention, generally designated 200 (commonly called a single-face corrugated structure). The structure 200 is formed in a similar manner as described above with respect to the structure depicted in FIG. 1. However, the first layer 10 is absent in structure 200. Thus, the structure 200 may be secured to a variety of first layers and provides a great deal of flexibility in manufacturing operations. For example, if printed material is placed on the outer side 11 of the first layer 10 described in FIG. 1, the printing could be done off line prior to securing the first layer 10 to the structure 200 illustrated in FIG. 2. Accordingly, a container manufacturer could use the structure 200 with a wide variety of first (or base) layers 10 (see FIG. 1) thereby giving rise to many advantages (e.g., reduced inventory). With such flexibility, the printed material on the first layer 10, as well as the thickness and material type for the first layer 10, could be varied while structure 200 remains consistent for a wide range of applications.

FIG. 3 illustrates a further alternative embodiment of the present invention, generally designated 300 (commonly called a double-wall corrugated structure). The structure 300 is formed in a similar manner as described above with respect to FIG. 1. However, a second fluted (i.e., corrugated) layer 320 and third flat layer 310 have been secured to the first flat layer 10 of FIG. 1. This second fluted layer provides a structure 300 with additional strength relative to the structure 100 depicted in FIG. 1. The first corrugated layer made up of 10, 20, and 30, and the second corrugated layer made up of 310 and 320 could be formed in two separate processes or in one continuous operation.

An advantage of the methods and structures according to the present invention is the manufacturing flexibility for container manufacturers. A manufacturer can purchase different quantities of the first layer 10, second layer 20, third layer 30 previously coated with layer 40, second corrugation layer 320, and third flat layer 310 In addition, the first flat layer 10 or third flat layer 310 can be printed off-line and in varying quantities to provide maximum flexibility with minimum inventory. The container manufacturer can then form the structures 100, 200, 300 described above for subsequent converting into container blanks (not shown). The blanks can then be formed into containers. Thus, the container manufacturer can buy the various layers 10, 20, 30 with various coatings 40, 310, 320 and form a wide range of structures and containers as needed.

A conventional forming technique involves thermoforming the container blank into the container shape. This technique involves applying heat and mechanical force concurrently to the container blank in a container-forming die. As mentioned, exemplary container thermoforming equipment is commercially available from Gralex Corporation of Lewis Center, Ohio.

Given the above detailed description and accompanying drawings, many other embodiments, features, modifications or improvements will become apparent to those skilled in the art. Such other embodiments, features, modifications and/or improvements are therefore considered to be a part of this invention, the scope of which is to be determined by the following claims. 

1. A corrugated structure comprising: a first flat layer; a first corrugated layer secured to said first flat layer; a second flat layer having a first side and a second side, wherein said first side is secured to said first corrugated layer on a side opposite of said first flat layer; a coating layer secured to said second side of said second flat layer, wherein said coating layer is a polymeric material having a melting temperature of at least about 450 degrees Fahrenheit and chloroform-soluble extractives of at most about 0.5 milligrams per square inch.
 2. The structure of claim 1 wherein said coating layer comprises polyethylene terephthalate (PET).
 3. The structure of claim 2 wherein said coating layer has a coat weight range of about 8 pounds per 3,000 square feet to about 30 pounds per 3,000 square feet.
 4. The structure of claim 1 wherein said coating layer comprises polymethylpentene (PMP).
 5. The structure of claim 4 wherein said coating layer has a coat weight range of about 5 pounds per 3,000 square feet to about 15 pounds per 3,000 square feet.
 6. A container blank formed from the structure of claim
 1. 7. The structure of claim 1 further comprising a second corrugated layer secured to said first flat layer on an opposite side from said first corrugated layer and a third flat layer secured to said second corrugated layer on an opposite side from said first flat layer.
 8. A corrugated structure comprising: a first corrugated layer; a first flat layer having a first side and a second side, wherein said first side is secured to said first corrugated layer; a coating layer secured to said second side of said first flat layer, wherein said coating layer is a polymeric material having a melting temperature of at least about 450 degrees Fahrenheit and chloroform-soluble extractives of at most about 0.5 milligrams per square inch.
 9. The structure of claim 8 wherein said coating layer comprises polyethylene terephthalate (PET).
 10. The structure of claim 9 wherein said coating layer has a coat weight range of about 8 pounds per 3,000 square feet to about 30 pounds per 3,000 square feet.
 11. The structure of claim 8 wherein said coating layer comprises polymethylpentene (PMP).
 12. The structure of claim 11 wherein said coating layer has a coat weight range of about 5 pounds per 3,000 square feet to about 15 pounds per 3,000 square feet.
 13. A corrugated structure comprising: a first flat layer; a first corrugated layer secured to said first flat layer; a second flat layer having a first side and a second side, wherein said first side is secured to said first corrugated layer on a side opposite of said first flat layer; a polymeric coating layer secured to said second side of said second flat layer.
 14. The structure of claim 13 wherein said polymeric coating layer is a polymer coating suitable for food contact.
 15. The structure of claim 13 wherein said polymeric coating layer is polyethylene terephthalate (PET).
 16. The structure of claim 13 wherein said polymeric coating layer is polymethylpentene (PMP).
 17. A method for forming a container comprising the steps of: providing a container blank comprising a corrugated structure having a first flat layer, a first corrugated layer secured to said first flat layer, a second flat layer having a first side and a second side, wherein said first side is secured to said first corrugated layer on a side opposite of said first flat layer, a coating layer secured to said second side of said second flat layer, wherein said coating layer has a melting temperature of at least about 450 degrees Fahrenheit and chloroform-soluble extractives of at most about 0.5 milligrams per square inch; providing a thermoforming machine; placing said container blank in said thermoforming machine; transferring heat and applying mechanical forces to said heated container blank to form said blank into a container shape using said thermoforming machine.
 18. The method of claim 17 wherein an outer surface of said first flat layer includes printed or graphic indicia.
 19. The method of claim 17 wherein said corrugated structure is formed using flexible manufacturing techniques wherein said first flat layer, said second flat layer previously coated with said coating layer and said first corrugated layer are selected from inventory materials to form said corrugated structure that is then formed into desired container blanks. 